A propulsion system of a spacecraft allows the spacecraft, during a mission, to change orbit, maintain course on a preferred orbit and control its attitude.
Such a propulsion system mainly comprises a propellant tank and propulsion units.
The tank is pressurized when the spacecraft launches.
Current propulsion systems comprise a tank including a sealing membrane delimiting an upper volume and a lower volume.
In this type of propulsion system, pressurized pressurizing gas is stored in the upper volume and the propellant is stored in the lower volume.
The pressurizing gas feeds the propulsion units with propellant.
During the mission, the gas will expand from 24 bars at 50° C. to 5.5 bars at 10° C., minimal pressure admissible for supplying the propulsion units.
Therefore, at the start of the mission, the tank is filled with a volume Vc,0 of propellant and a volume Vg,0 of pressurizing gas. The quantity of gas is determined so that during the mission there is the following equality: Vg,0/Vg,f=(Pf/P0)*T0/Tf where Vg,f is the volume of gas on completion of the mission when the tank contains no more propellant, P0 is the pressure in the tank when it is filled to its maximum capacity at the temperature T0 and Pf is the pressure in the tank at the temperature Tf when the tank is empty.
A problem is that the maximum volume Vc,0 of propellant is limited because the tank contains gas to respect the constraints hereinabove. So, the duration of a mission is impacted by the capacity of the tank which is such that Vc,0=Vg,f−Vg,0.